Ever increasing sophistication of vehicles, from cars to trucks, leaves less space available in the dashboard-firewall area, the typical location for windshield wiper mechanisms. Traditionally, those mechanisms use one electric motor to rotate a gear containing a crank pin connected to each windshield wiper blade so that as the pin rotates the wipers sweep back and forth. Each blade may be connected to a rocker arm so that the blade orientation on the arm changes as the blade sweeps the windshield, increasing the cleared area.
Multi-speed wiper systems have been in use for some time; so too, intermittent wiper systems that have a variable delay by which the blades do not sweep continuously but temporarily stop at or near their parked position, near the bottom of the windshield.
Not surprising, the mechanical arm that links to the blades and the motor takes up space, often substantial, under the dashboard. Moreover, the area near this moving arm must be kept clear of wires and the like. Servicing this type of wiper system is difficult, as well, by reason of limited space under the dashboard.
Some wiper systems use separate electric motors for each blade, an arrangement that obviously releases space in the dashboard-firewall area. However, synchronizing the motors can be a problem, something addressed in U.S. Pat. No. 5,216,340, assigned to the assignee of this application.
Special synchronization problems arise when efforts are made to optimize the clearing performance by the wipers. When the wipers are not in use, they should be parked in a location that does not obstruct the driver's view. When the wipers are operating, as much of the windshield as possible should be cleared, especially the windshield in front of the driver. To optimize the cleared area, so-called "pantograph" arms and blades are used. This permits the blades to move transversely along the windshield, instead of in a generally radially, yet park vertically in the middle of the windshield or at its outboard ends. As a practical matter, this means that the blades must overlap considerably when parked.
Complicating the blade synchronization process, besides variations in motor speed, snow and ice can impede the movement of the blades unevenly, causing one blade to move faster than the other. The blades, if too unsynchronized may clash, especially when blade overlap is high.